Color image pickup apparatus

ABSTRACT

A color image pickup apparatus having: an image pickup device in which a color filter array is provided, the color filter array being composed of color filters of three or more colors disposed in such a manner that, assuming that the horizontal scanning directional pitch of the color filters is PH and the vertical scanning directional pitch of the same is Pv, the color filters of the same color are disposed at a horizontal scanning directional pitch of 2PH and a vertical scanning directional pitch of 2Pv while being offset by PH in the horizontal scanning direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a color image pickup apparatus such asa still video camera and a video camera.

2. Related Background Art

Hitherto, in order to frame-photograph (obtain odd and even fieldinformation items) a still image by a still video camera or the like,there has been a necessity of using a color filter image pickup devicehaving a color filter which is operated at a period of two pixels asshown in FIGS. 1A and 1B. The reason for this is in that it is necessaryto make the outputs from the odd fields and even fields the same becausethe conventional image pickup device alternately reads the odd rows andeven rows as shown in FIGS. 1A and 1B.

However, if the image pickup device having the color filter arranged asshown in FIGS. 1A and 1B is used, a luminance signal and a chrominancesignal can be deduced by using data of two rows positioned alternately,for example, the first and third rows in the odd field. The second andfourth rows in the even field must be used. As a result, the verticaldirectional distance between data items is enlarged, causing thecorrelation in the vertical direction to be reduced. Therefore, thequantity of generation of pseudo color undesirably increases.

Another problem arises in that a multiplicity of 1H (horizontal scanningperiod) delay lines are necessary to deduce the luminance signal and thechrominance signal for use in the signal process.

FIG. 2 illustrates the positions at which carrier components aregenerated in the vicinity of the base band of an image pickup deviceprovided with the above-described color filter. In either of the casesshown in FIGS. IA and IB, the carrier of the luminance signal isgenerated at positions (±1/PH, 0) assuming that the horizontal scanningdirectional pitch of the color filters of the image pickup device is PH.Furthermore, the carrier of the chrominance signal is generated atpositions (±1/2PH, 0) because the pitch of the filters of the same colordisposed in the horizontal direction is 2PH.

The luminance signal obtainable from the above-described image pickupdevice is arranged to have its band to a frequency of 1/2PH inaccordance with the theorem of sampling. Therefore, in order to preventthe reflected distortion of the luminance signal, it is ideal that theoptical low-pass filter to be disposed in front of the image pickupdevice is able to make all of the frequency components higher than 1/2PHto be zero. However, the carrier of the chrominance signal is generatedat the horizontal frequency fH=±1/2PH as shown in FIG. 3. As a result,if the optical low-pass filter having the above-described frequencycharacteristics is used, the pseudo color is generated due to thereflection of the chrominance signal. Therefore, as shown in FIG. 3, thefrequency characteristics of the optical low-pass filter must have theband which is lower than fH=1/2P_(H) by a degree corresponding to thechrominance signal. As a result, a problem arises in that the obtainableresolution is lower than the principle resolution limit.

FIG. 4A illustrates the structure of a conventional optical low-passfilter for use in a solid image pickup device in which the color filtersare arranged as shown in FIG. 1. Referring to FIG. 4A, an opticallow-pass filter 70 comprises a birefringence plate 71 for dividing alight beam into two beams, the light beam being a beam made incidentupon by making an angle of 90° from the horizontal direction by adistance of PH. The low-pass filter 70 further comprises a phase plate72 for converting linearly polarized light into circularly polarizedlight. The low-pass filter 70 further comprises another birefringenceplate 73 for dividing a light beam into two beams, the light beam beinga beam made incident upon by making an angle of 90° from the horizontaldirection by a distance of PH/2. The transfer characteristic (MTF) H1 ofthe above-described optical low-pass filter is expressed by thefollowing equation:

    H1 (fx, fy)=|cos (π/2 PH fx)·cos (πPH fx)|(1)

The above-described characteristic can be graphed as shown in FIG. 4B.The characteristic on the frequency space is as shown in FIG. 4C. Dottedlines 74a, 74b, 75a and 75b show the frequencies at which the opticallow-pass filter 70 traps. As can be seen from FIG. 4C, carrier frequencyfH=±1/PH of the luminance signal and carrier frequency fH=±1/2PH of thechrominance signal are trapped. As can be seen from Equation (1) or FIG.4B, the optical low-pass filter having the above-describedcharacteristics is as follows: the MTF is 0 at the carrier frequencyfH=±1/2PH of the chrominance signal; and the transference characteristicis-15 dB at about 85 of the frequency. Therefore, the number of theresolution lines to the resolution limit fH=1/2PH cannot be obtained.

SUMMARY OF THE INVENTION

To this end, an object of the present invention is to provide a colorimage pickup device in which generation of false color can be prevented,resolution of the luminance signal can be obtained to the theoricallimit and a frame image can be formed.

In order to achieve the above-described object, the color image pickupapparatus according to the present invention is constituted as any onethe following structures (1) to (7):

(1) A color image pickup apparatus having an image pickup device inwhich a color filter array a is provided:

a. a color filter array composed of color filters of three or morecolors disposed in such a manner that, assuming that the horizontalscanning directional pitch of the color filters is PH and the verticalscanning directional pitch of the same is Pv, the color filters of thesame color are disposed at a horizontal scanning directional pitch of2PH and a vertical scanning directional pitch of 2PH while being offsetby PH in the horizontal scanning direction.

(2) A color image pickup apparatus according to (1) including: an imagepickup device having an optical low-pass filter provided on the frontsurface thereof, the optical low-pass filter being constituted bylaminating a first optical member for dividing a light beam madeincident upon by distance P₁ while making an angle of 45° from thehorizontal scanning direction into two light beams, a second opticalmember for dividing a light beam made incident upon by distance P2 whilemaking an angle of 90° from the horizontal scanning direction into twolight beams and a third optical member for dividing a light beam madeincident upon by distance P1 while making an angle of 135° from thehorizontal scanning direction into two light beams, the optical low-passfilter disposed to meet the following conditions: ##EQU1##

(3) A color image pickup apparatus having a color filter array, fromwhich the carrier of a chrominance signal is not generated and which isdisposed on the horizontal frequency axis in a 2D-frequency spacearranged in the horizontal direction and the vertical direction.

(4) A color image pickup apparatus according to (3) and having anoptical low-pass filter for trapping a portion in the vicinity of theposition of the carrier of a luminance signal and that of a chrominancesignal in a 2D-frequency space arranged in the horizontal direction andthe vertical direction, wherein the optical low-pass filter is disposedon the front surface of the image pickup device.

(5) A color image pickup apparatus according to any one of (1), (2), (3)and (4), wherein an output from the image pickup device is temporarilyrecorded in a memory so that frame information is formed in response toa read signal from the memory.

(6) A color image pickup apparatus having the following elements a, band c:

a: an image pickup device in which the horizontal directional pixelpitch is PH and the vertical directional pixel pitch is Pv;

b: a color filter array formed into an offset structure and provided forthe image pickup device, the color filter array being composed of colorfilters of three or more colors disposed in such a manner that the colorfilters of the same color are disposed at a horizontal scanningdirectional pitch of 2PH and a vertical scanning directional pitch of2Pv while being offset by PH in the horizontal scanning direction.

c: an optical low-pass filter composed of; a first optical member fordividing an incidental light beam into two light beams away from eachother in a direction of 45° from the horizontal direction by distance P;and a second optical member for dividing an incidental light beam intotwo light beams away from each other in a direction of 90° from thedirection in which the first optical member divides the light beam bydistance P, the optical low-pass filter being provided for an imagepickup optical system and meeting the following conditions: ##EQU2##

(7) A color imaging apparatus according to (6) further comprising asignal processing means constituted by a memory for temporarily storingan output from the image pickup device and a control portion forcontrolling the memory, the signal processing means forming frameinformation from the contents stored in the memory.

According to the embodiments (1) to (7), the resolution limit offH=1/2PH can be obtained by virtue of the provided color filter arrayformed into the offset structure. The carrier of the chrominance signalcan be deleted by the optical low-pass filter so that generation offalse color is prevented. Furthermore, according to the structures (5)and (7), frame information can be formed by the provided signalprocessing means.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate an example of the arrangement of colorfilters according to a conventional structure;

FIG. 2 illustrates frequency spatial characteristics of the conventionalstructure;

FIG. 3 illustrates the characteristics of an optical low-pass filter foruse in the conventional structure;

FIGS. 4A to 4C illustrate the operation of the optical low-pass filterfor use in the conventional structure;

FIG. 5 illustrates the arrangement of color filters according to a firstembodiment of the present invention;

FIG. 6 illustrates the frequency spatial characteristics according tothe first embodiment of the present invention;

FIGS. 7A to 7D illustrate the operation of the optical low-pass filterfor use according to the first embodiment of the present invention;

FIG. 8 is a block diagram which illustrates the overall structureaccording to the first embodiment of the present invention;

FIG. 9 is a block diagram which illustrates a matrix circuit 19according to the first embodiment of the present invention;

FIG. 10 is a first structural schematic view of a serial memory 9according to the first embodiment of the present invention;

FIG. 11 is a timing chart of the memory shown in FIG. 10;

FIG. 12 is a second structural schematic view which illustrates theserial memory 9 according to the first embodiment of the presentinvention;

FIG. 13 is a timing chart of the memory shown in FIG. 12;

FIG. 14 illustrates the arrangement of the color filters according tothe second embodiment of the present invention;

FIGS. 15A and 15B illustrate the operation of the optical low-passfilter for use according to the second embodiment of the presentinvention; and

FIG. 16 illustrates the overall structure according to the secondembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described.

FIG. 5 illustrates the arrangement of color filters for use in a colorimage pickup apparatus according to a first embodiment of the presentinvention. The overall body of the color filter is called a "colorfilter array" hereinafter.

As shown in FIG. 5, a color filter array 1b (see FIG. 8) is composed ofpure R, G and B filters. Assuming that the horizontal directional pitchof the color filters is PH and the vertical directional pitch of thesame is Pv, the color filters R, G1, G2 and B of the correspondingcolors are formed into an offset sampling structure which is arranged insuch a manner that they are disposed at a horizontal directional pitchof 2PH, a vertical directional pitch of 2Pv having a horizontaldirectional offset quantity of PH.

FIG. 2 illustrates the positions at which the carrier component isgenerated in the vicinity of the base band of the image pickup devicewhich employs the color filter array structured as described above.

As shown in FIG. 2, the carrier of the luminance signal is generated atpositions (±1/PH, 0), while the carrier of the chrominance signal isgenerated at positions (±1/2Pa, 1/4Pv). As can be clearly seen from aresult of a comparison made with FIG. 2, the carrier of the chrominancesignal is not present on the axis FH but is vertically shifted by adistance of ±1/4PH. Therefore, it is disposed away from the base band,causing the generation of the pseudo color due to the reflection of thechrominance signal to be prevented. Furthermore, since there is nocarrier signal of the chrominance signal on the fx axis, luminancesignals can be obtained to the resolution limit frequency, that is,fH=1/2PH.

FIGS. 7A to 7D illustrate the structure of the optical low-pass filteraccording to this embodiment.

Referring to FIGS. 7A and 7D, an optical low-pass filter 30 comprises afirst optical member composed of a birefringence plate 31 for dividing alight beam into two beams, the light beam being a beam made incidentupon by making an angle of 45° from the horizontal direction by adistance of P1. The low-pass filter 30 further comprises a secondoptical member composed of a birefringence plate 32 for dividing a lightbeam into two beams, the light beam being a beam made incident upon bymaking an angle of 90° from the horizontal direction by a distance ofP2. The low-pass filter 30 further comprises a third optical membercomposed of a birefringence plate 33 for dividing a light beam into twobeams, the light beam being a beam made incident upon by making an angleof 135° from the horizontal direction by a distance of P1. Furthermore,the optical low-pass filter 30 meets the following conditions: ##EQU3##

If P1 exceeds the lower limit of Inequality (2), the generation of thereflection distortion, in particular, the generation of the pseudo colorcannot be prevented. If the same exceeds the upper limit, a satisfactoryresolution cannot be obtained. Furthermore, is P2 exceeds the upperlimit of Inequality (3), a satisfactory resolution also cannot beobtained. The transfer characteristic (MTF) of the optical low-passfilter 30 can be expressed by the following equation: ##EQU4##

In a case of a frame of an NTSC system having an aspect ratio of 3:4, asolid image pickup device having about 640 effective pixels in thehorizontal direction and about 480 effective pixels in the vertical, asshown in FIG. 5, holds the following relationship:

    PH=Pv                                                      (5)

According to this embodiment, the relationship is arranged as follows:##EQU5##

The transfer characteristic with respect to the fx axis displayed by thestructure constituted as described above is shown in FIG. 7C. The samein a two-dimensional frequency space is shown in FIG. 7D. Dotted lines34a, 34b, 35a, 35b, 36a and 36c show the frequencies at which theoptical low-pass filter 30 traps. As can be seen from FIG. 7D, thecarrier frequencies of the luminance and chrominance signals aretrapped. Furthermore, as can be seen from FIG. 7C, the frequencycomponents higher than the resolution limit frequency fH=1/2PH aresatisfactorily prevented. Therefore, the reflection distortion of theluminance can be prevented. In addition, as can be clearly seen fromEquations (4), (5) and (6), the decay of the transfer characteristics isrestricted within-15 dB in a frequency range of |fH|≦1/2P_(H).Therefore, the desired resolution can be substantially secured to thelimit resolution frequency 1/2PH.

A method of obtaining an image signal according to this embodiment willnow be described.

FIG. 8 is a block diagram which illustrates the overall structureaccording to this embodiment, where reference numeral 30 represents anoptical low-pass filter. Reference numeral 1a represents a solid imagepickup device CCD, 1b represents a color filter array provided for thesolid image device 1a and 2 represents a correlation double samplingcircuit. Reference numeral 3 represents a color separation circuit(C-SEP circuit) and 4 represents a WB block for white-balance-adjustinga signal which has been subjected to the color separation process.Reference numerals 5 and 7 represent switches for selecting either ofthe two outputs and 6 represents a signal processing block forperforming a gamma process, a white clip process, a blanking process anda pedestal level setting process. Reference numeral 8 represents ananalog-to-digital converter (A/D converter) and 9 represents a serialmemory block. Reference numerals 10 and 11 represent digital-to-analogconverters (D/A converters) and 12 represents a memory controller forcontrolling the analog-to-digital converter (A/D converter), the serialmemory block and the D/A converter. Reference numeral 13 represents aclock generating circuit for generating a variety of pulses and 14represents an adder. Reference numerals 15, 16, 17 and 18 representsample holding circuits and 19 represents a matrix circuit forgenerating luminance signal (Y) and chrominance signals (R-Y, B-Y) fromthe outputs from the elements 14 to 18.

FIG. 10 is a structural schematic view which illustrates the serialmemory block 9. FIG. 11 is a timing chart of the operation performed bythe memory controller.

The operation of the present invention will now be described withreference to FIGS. 8, 10 and 11.

An image signal transmitted from the solid image pickup device shown inFIG. 8 is subjected to a process in which its reduction noise iseliminated by the correlation double sampling circuit 2 before it issupplied to the color separation circuit 3. The image output from thesolid image pickup device 1a is separated into three primary colorsignals, that is, R, G and B signals by the color separation circuit 3.Then, the WB block 4 performs the white balance adjustment operation.However, since the solid image pickup device 1a is arranged in such amanner that the color filters thereof are arranged as shown in FIG. 5,only R and G signals can be obtained in the odd fields and only B and Gsignals can be obtained in the even fields. Therefore, the B signaltransmitted from the WB block 4 in the odd field and the R signaltransmitted from the WB block 4 in the even field are false informationwhich cannot be used. Therefore, the switch 5 selects the R signal inthe odd field while the same selects the B signal in the even field.Switching pulses Fv causing the above-described selection to beperformed are transmitted from the clock generating circuit 13. Assumingthat a signal defined by alternating the selected signals R and B ateach IV (vertical scanning period) is expressed by R|B, symbol "|" isused to express the plane succession hereinafter.

Then, the RB signal, together with another output G from the WB block 4,is supplied to the signal processing block 6 so as to be subjected tothe gamma, white clip, blanking and pedestal level setting processes.

The output G and the R|B signal transmitted from the signal processingblock 6 are switched over in units of a pixel in response to pulse SHlby the switch 7 so that signal G1, R|G2, B (hereinafter abbreviated to"G, R|B)" which again corresponds to the color filter arrangement of thesolid image pickup device 1, where mark "," shows that the subjectsignal is a dot successive signal. The SHl pulses are transmitted fromthe clock generating circuit 13.

The dot-successive signal G, R|B formed by means of the switch 7 isconverted into a digital signal by the A/D converter 8 before it issupplied to the serial memory block (S. MEM) 9. Then, the two systems ofthe output from the serial memory block 9 are converted into analogsignals by the D/A converters 10 and 11. At this time, clocks PAD andPDA for use in the A/D and D/A converters and the memory control pulseare transmitted from the memory controller 12.

The operation of the serial memory 9 will further be described withreference to FIGS. 10 and 11.

Referring to FIG. 10, reference numerals 20 to 22 represent serialmemories (according to this embodiment, three chips are necessary topossess a memory capacity capable of storing data of all pixels of theCCD which is the solid image pickup device 1). Reference numeral 23-1represents a switch for switching over the output from each of thememories so as to output it to the D/A converters 10 and 11. Since theinput of the output from the CCD is commenced at to as shown in FIG. 11(2), the output from the CCD is stored in a memory (1st Chip 20) of thefirst chip of the serial memory 9 in such a manner that the level ofwrite enable signal WEI is raised so that the memory 20 is enabled.Furthermore, write reset signal RSTWl is used to reset the write addressof the memory so that writing is commenced at address zero (the left endportion of the first row designated by reference numeral 20 shown inFIG. 10). As a result, a (B, R) signal of the CCD output (odd field)shown in FIG. 10 (2) is stored on the memory 20 shown in FIG. 10 asillustrated. Then, the level of the write enable signal WEI is loweredwhen the storage capacity of the memory has been filled at t1. As aresult, the memory 20 is disabled. At this time, in response to theenable signal WE2 shown in FIG. 11, the memory (2nd Chip 21) of thesecond chip of the serial memory 9 is enabled so that output signals inthe CCD odd fields ensuing t1 are, as shown in FIG. 10, stored startingfrom address zero in response to the output pulse RSTW2 shown in (9).Then, the level of the write enable signal WE2 is lowered in blankingperiod Kx before time t3 at which the odd field starts so as to maintainthe address at t2. As a result, writing to the memory 21 is inhibited.In a case where each of the memories 20, 21 and 22 is a serial dynamicmemory arranged to have the blanking period KH which is longer thanpredetermined time Ko, a resetting operation is sometimes necessary.Therefore, the blanking period KH of the CCD image output is set to beshorter than a time in which data can be held while holding the address(KH<KO). Even if KH is set regardless of the TV-rate V blanking periodso as to perform writing to the memory, no problem takes place by makingit to be the normal V blanking period at the time of the readingoperation.

When the image period of the even field is commenced at t3, the level ofthe write enable signal WE2 shown in FIG. 11 (8) is again raised so thatdata of the signal (G2, B) is written to time t4 at which the capacityof the memory 21 is filled. At time t4, the level of the write enablesignal WE2 is lowered so as to disable the memory 21. Then, the level ofthe write enable signal WE3 shown in (12) is raised so as to generatepulse RSTW3 shown in (13). As a result, even field image signals ensuingfrom t4 are written to a memory (3rd Chip) 22 of the third chip.Simultaneously with the completion of the even field image signals attime t5, the memory 22 is disabled in response to the write enablesignal WE3 so that the writing operation is completed.

The reading operation from the serial memory 9 will now be described.First, the switch 23-1 is brought to an open state by bringing it intocontact with b. At time t6, the level of read enable signal RE2 shown in(10) is raised so as to output read reset pulse RSTR2 shown in (11). Asa result, reading of the memory 21 is commenced. At this time, theswitch 23-1 is opened and the output from each of the memories 20 and 22is in a high impedance state because the level of each of the readenable signals RE1 and RE3 is low. Therefore, no signal is transmittedto 10 and 11. Then, the level of the RE1 is raised at ts so that thepulse RSTRI is transmitted. As a result, data in the memory 20 is readout so as to be transmitted to 10. Simultaneously, the switch 23-1 isconnected to a, the output from the memory 21 is read to be supplied to11. At this time, since the address of the memory 21 has been proceededby 1H, address for data stored (X rows from the first row) in a periodbetween t1 and t2 of the WE2 shown in (8) has been proceeded. Therefore,the address shows (G2, B) data starting row (X+1) of 21, causing the(G2, B) signal to be transmitted to 11. Then, the switch 23-1 isconnected to b at t9 so as to be opened. Furthermore, the level of theRE3 is raised so as to output pulse RSTR3. As a result, data-reading ofthe memory 22 is commenced. Therefore, data (G2, B) output from thememory 22 is supplied to 11. At t10, the switch 23-1 is connected to cso that the RSTR2 pulse is again transmitted, causing a signal from theaddress zero to be transmitted to 10. At t11, the image period for thefirst field is ended before the switch 23-1 is connected to b.Furthermore, the level of each of the RE2 and RE3 is lowered so as todisable all of the memories. Then, reading of the second field isperformed. First, similarly to the process for the first field, thelevel of the RE2 is raised at t12 so as to transmit the pulse RSTR2. Atthis time, the connection established between the switch 23-1 and b ismaintained, causing no signal to be transmitted to 10 and 11. Then, thelevel of the RE1 is raised at t14 so as to transmit the pulse RSTR1. Att15, 1H later t14, the switch 23-1 is connected to a, causing output(G1, B) from the memory 20 to be transmitted from address zero to theD/A converter 11. Furthermore, data (G2, B) in 21 is transmitted to theD/A converter 12 at t15. Thus, the second field is read by delaying by 1H in order to secure interlace from the signals in the first field. Thatis, signals read from the second row of the memory 20 to be transmittedto 10 are significant, while signals read from the (X+1)-th row of thememory 21 to be transmitted to 11 are significant. Therefore, assumingthat the length of a period from t7 to t8 is mH, the length of a periodfrom t13 to t14 is (m-1)H. When reading of the final row z has beencompleted at t16, the switch 23-1 is connected to b. Furthermore, thelevel of the RE3 is raised so as to transmit pulse RSTR3, causing theoutput supplied to 11 to be switched over to the first column of thememory 22. Then, the switch 23-1 is connected to C at t17 so as toswitch over the output to be supplied to 10 to the memory 21.Simultaneously, the pulse RSTR2 is transmittted so that data reading iscommenced at the first row of the memory 21. At this time, the period inwhich the REl is enabled is nH which is the same as that in the firstfield. Therefore, the output is switched over to the memory 21 afterreading of the memory 20 has been completed. Therefore, the lack ofinformation at the boundary can be prevented. On the other hand, aperiod t13 to t17 from the first transition of the VP shown in FIG. 11(1) is (m+n-1)H which is shorter than the length from t7 to t10 Of thefirst field by 1H.

Then, outputting is continued to t18 at which the switch 23-1 isconnected to b so that the switch 23-1 is opened. Simultaneously, thelevel of each of the RE2 and the RE3 is lowered, causing the memories 21and 23 to be brought into a high impedance state. Thus, the outputoperation of the image signal is completed.

In the second field, reading of data (G2, B) is commenced at t15, whilereading of data (G2, R) is commenced at t14. Therefore, the readcommencement time is delayed by 1H. Furthermore, a false signal isundesirably read out because data (G1, R) is not present at the time ofreading data (G2, B) from the final row. Therefore, reading of data (GI,R) and (G2, B) in the second field is reduced by 1H from the imageperiod for the significant pixels. Simultaneously, if the image periodis different between the first field and the second field, a partialflicker takes place on the final row (row Z). Therefore, the first fieldis also arranged in such a manner that the period in which output signalis transmitted is shortened by 1H for both (G1, R) and (G2, B). That is,assuming that the length of the period from t17 to 18 is OH, the periodfrom t10 to t11 is (o-1)H. Therefore, time t7 to t11 and time t13 to t18from the first transition of the VP are (m+n+o-1)H for both first andsecond fields. Furthermore, a false signal will be generated becausereading of the memory 20 in the first field is performed earlier by 1H.Therefore, the output form the memory 20 from t10 to t15 is opened by aswitch 23-2 shown in FIG. 12 so as to delete the subject data.

Furthermore, signals except for period (n+o-1)H may be muted in a periodfrom t8 to t11 and a period from t15 to t18 by using a blanking pulse asshown in (18) so as to delete the false signal and to prevent theflicker. As an alternative to the deletion of the false signal, a methodmay be employed in which the row Z in the memory 22 is read twicesuccessively so as to output to the final row of the memories 21 and 22in the first field and the memory 21 in the second memory.

On the other hand, setting of the write completion timing, readcommencement timing, timing of the completion of reading the first fieldand timing of the commencement of reading the second field may bearbitrarily made to suit the specifications of the employed serialmemory or the image pickup device to which the present invention isadapted. By approximating the timing of each of the operations, thephotographing speed can be raised.

Furthermore, by completing the switching of the switches 23-1 and 23-2within the H-=blanking period of the image signal, generation ofundesirable noise can be prevented. FIGS. 13 (16) and (17) are timingcharts of each of the outputs (outputs to the D/A converters 10 and 11).

The digital signals transmitted to the D/A converters 10 and 11 asdescribed above are converted into analog signals (G1, R) and (G2, B)before they are transmitted to the ensuing analog signal processingcircuits. First, in 14, the signals (G1, R) and (G2, B) are added toeach other so that luminance signal YH having a high band component isdeduced. In 15 and 16, each of the signals (G1, R) and (G2, B) issample-held by the SH1 pulse so that G1 and G2 are deduced. Then, in 17and 18, the signals (G1, R) and (G2, B) are sample-held by SH2 pulse sothat R and B signals are deduced which are then transmitted to thematrix circuit portion 19. In 19, G1 and G2 are averaged by the adder 24as shown in FIG. 9 so that G is deduced before the difference between G1and R and the difference between G2 and B are calculated by subtracters25 and 26 so that G - R and G - B are deduced. Then, G - R, G, G - B aretransmitted to a YL MATRIX 27 so that reduced luminance signal YL isdeduced, while G - R and G - B are transmitted to a C MATRIX 28 so thatchrominance signals R - Y and B - Y are deduced.

On the other hand, adders 29 and 30 add G1 to R and also add G2 to Bbefore an adder 31 adds the outputs from the adders 29 and 30 to eachother so that reduction component YHL of the output YH from the adder 14is deduced. Furthermore, a subtractor 32 deduces the difference YH - YHLbetween YH and YHL. The output G from the adder 24 is made to be asignal delayed by 1H by a 1H delay line 34 before the difference from G,that is, VAPC denoting the vertical high band component, is deduced by asubtracter 35. Then, YL and YH - YHL are added to each other by an adder33 before VAPC is added by an adder 36 so that luminance signal Y:YHH+YL+VAPC is obtained.

As described above, according to this embodiment, the memory can furthersimply be controlled by using the serial memory 9 so that the memorycontrol 12 can easily be designed.

Furthermore, if a high speed a synchronous read/write enable high speedFIFO serial memory is employed, reading (at t6 in a case of the memory21) can be commenced during the memory writing operation (in a periodfrom t1 to t4 in a case of the memory 21). Therefore, the systemoperational speed can be raised further.

A modification to this embodiment will now be described.

The overall structure according to this modification is arranged to bethe same as that shown in FIG. 8. However, in the flow of the signaltransmission subsequently to the memory, signals designated inparentheses are transmitted. Description will now be made with referenceto FIGS. 12 and 13. First, as shown in FIG. 13 (2), supply of the outputfrom the CCD 1 through the A/D converter 8 is commenced at t1.Therefore, the above-described output is stored starting form the(X+1)-th row of the memory 21 in such a manner that the level of thewrite enable signal WE2 shown in FIG. 13 (8) is raised at t0 which is 1Hbefore it so as to be the enable state. Then, writing is commenced fromaddress zero (the left end of the first row of the memory 21 shown inFIG. 12) after the write address of the memory has been reset inresponse to the write reset signal RSTW2, where 1 =x. As a result, (G1,B) signals of the CCD output (odd field) are stored as illustratedsubsequently to the (X+1)-th row on the memory 21 shown in FIG. 8. Then,the level of the WE2 is lowered at t2 at which the storage capacity ofthe memory 21 is filled. As a result, the memory 21 is disabled. At thistime, the memory 22 is enabled in response to the write enable signalWE3 shown in (12) so that output signals from address zero in the CCDodd field ensuing t2 is stored in the memory 22 as shown in FIG. 12 inaccordance with the output of the pulse RSTW3 shown in (13). The levelof the WE3 is lowered from t3 at which the image period in the odd fieldis completed so that the memory 22 is disabled. Then, the level of WE1shown in (4) is raised at t4 at which the image period of the even fieldis commenced. As a result, data of the signal (G2, B) is written untilt5 at which the capacity of the memory 20 is filled. At t5, the level ofthe WE1 is lowered so that the memory 21 is disabled. Then, the level ofthe WE2 shown in (8) is again raised so that the pulse RSTW2 shown in(9) is generated. As a result, even field image signals from t5 arewritten from the first row of the memory 21 to the (X - 1)-th row of thesame. Simultaneously with completion of the even field image signal att₆, the memory 21 is disabled in response to the WE2 so that the writingoperation is completed. An operation of reading data from the serialmemory 9 will now be described. First, the switch 23 - 1 is connected tob so as to be opened. At t7, the level of the read enable signal RE2shown in (10) is raised so that the read reset pulse RSTR2 istransmitted to commence reading of the memory 21. At this time, theswitch 23-1 is opened, the level of each of the RE1 and RE2 is low andthe outputs from the memories 20 and 22 are high impedance, and nosignal is transmitted to 10 and 11. Then, the level of the RE1 is raisedat t9 so that the RSTR1 pulse is transmitted. As a result, data in thememory 20 is read out so as to transmit it to 10. Simultaneously, theswitch 23-1 is connected to a so that the output read out is supplied to11. At this time, since the address of the memory 21 proceeds by 1H, theaddress has been proceeded by the degree corresponding to the storagemade from t5 to t6 of the WE2 shown in (8). Therefore, since the addressshows the (X+1)-th row where there is data of (G1, R) of the memory 21shown in FIG. 12, the signal (G1, R) is transmitted to 11.

Then, the switch 23-1 is connected to b at t10 so as to be opened.Simultaneously, the level of the RE3 is raised so that the pulse RSTR3is transmitted. As a result, reading of data from the memory 22 iscommenced. As a result, data (G1, R) which is the output from the memory22 is transmitted to 11. At t11, the switch 23-1 is connected to c, andsimultaneously the pulse RSTR2 is again transmitted so that the signalsare transmitted from address zero of the memory 21 to 10. When the imageperiod in the first field has been ended at t12, the switch 23-1 isconnected to b so that the level of each of the RE2 and RE3 is lowered.As a result, each of the memories is disabled.

Then, reading of the second field is performed. Similarly to the firstfield, the level of the RE2 is raised at t13 so that the pulse RSTR2 istransmitted. At this time, the connection established between the switch23-1 and b is maintained. Therefore, no signal is transmitted to 10 and11. At t15, the switch 23-1 is connected to a, causing the level of theREl to be raised. As a result, the pulse RSTRI is transmitted.Therefore, the output (G2, B) from the memory 20 is, from address zero,transmitted to 10, while data (G1, R) in the memory 21 is transmitted to11. However, it is necessary for the second field to perform readingwhile delaying by 1H for the purpose of having interlace with respect tothe signal in the first field. That is, it is necessary to read theoutput to be supplied to 11 from the second row of data (G1, R), thatis, the (X+2)-th row. Therefore, assuming that the length of the periodfrom t7 to t8 is mH, the length of the period from t13 to t14 is (m+1)H.By making the period from ts to t9 to be the same as the period from t14to t15, the address of the memory 21 is set to the left end of thesecond row (X+2) of data (G1, R). Then, the switch 23-1 is connected tob at t16 so that the level of the RE3 is raised. As a result, the pulseRSTR3 is transmitted. According to this modification, t16 is set in sucha manner that a period from t14 to 16 is (n-1)H. Thus, it is shorterthan the period from t8 to t10 in the first field by 1H Therefore, theperiod from t7 to t10 and that from t13 to t16 is the same as (n+m)H.Therefore, the subject point is the point at which reading of data (G1,R) of 2 has been completed at t16. That is, at t16, data (G1, R) istransmitted to 11 from the 2nd Chip output while preventing lack ofinformation at the boundary to the Chip output. Therefore, the switch23-1 is connected to c at t17 so as to lower the level of the RE1. As aresult, the pulse RSTR2 is again transmitted. Therefore, the output tobe supplied to 10 is switched over from the memory 20 to 21, the thusselected output being continued to t18. At t18, the switch 23-1 isconnected to b so as to be opened. Simultaneously, the level of each ofthe RE2 and RE3 is lowered so that the memories 21 and 22 are brought tohigh impedance state. Thus, the output operation of the image signal iscompleted. In the second field, although reading of data (G2, B) iscommenced from the first row in the second field, reading of data (G1,R) is commenced from the second row. Therefore, the reading time delaysby 1H, causing a false signal to be read out since there is no (G1, R)data at the time of reading the final row of data (G2, B). As a result,reading of data (G1, R) and (G2, B) in the second field is reduced by adegree corresponding to 1H in comparison to the image period of thesignificant pixel. Furthermore, if the image period is different fromthat of first field, undesirable partial flicker takes place. Therefore,reading of data (G1, R) and (G2, B) in the first field is reduced by adegree corresponding to 1H. That is, assuming that the length from aperiod from t16 to t18 is 0H, a period from ts to t12 and that from t14to t16 are the same as (n+0-1)H in both first and second fields.Furthermore, the signal may be muted in the periods other than theperiods from t9 to t12 and that from t15 to t18 in response to theblanking pulse shown in (18) for the purpose of deleting falseinformation and preventing the flicker. As an alternative to thedeletion of the false information, an approximation process may beemployed in which the row Z of the memory 22 is read twice successively.On the other hand, setting of the write completion timing, readcommencement timing, timing of the completion of reading the first fieldand timing of the commencement of reading the second field may bearbitrarily made to suit the specifications of the employed serialmemory or the image pickup device to which the present invention isadapted. By approximating the timing of each of the operations, thephotographing speed can be raised. Furthermore, by completing theswitching of the switches 23-1 within the H-blanking period of the imagesignal, generation of undesirable noise can be prevented. FIGS. 13 (16)and (17) are timing chart of each of the outputs (outputs to the D/Aconverters 10 and 11). The digital signals transmitted to the D/Aconverters 10 and 11 as described above are converted into analogsignals (G2, B) and (G1, R) before they are transmitted to the ensuinganalog signal processing circuits. First, in the adder 14, the signals(G1, R) and (G2, B) are added to each other so that luminance signal YHhaving a high band component is deduced. In S/H 15 and 16, each of thesignals (G2, B) and (G1, R) is sample-held by the SHl pulse so that G2and G1 are deduced. Then, in S/H 17 and 18, the signals (G2, B) and (G1,R) are sample-held by the pulse SH2 so that B and R signals are deducedwhich are then transmitted to the matrix circuit portion 19. The ensuingoperation of the matrix circuit 19 is arranged similarly to theabove-made description.

According to this embodiment, although the serial memory is employed asthe memory, a random access memory may also be employed. Furthermore,individual memories may be employed to correspond to the signals G1, G2,R and B.

FIG. 14 illustrates the arrangement of color filters of the solid imagepickup device of the color image pickup apparatus according to a secondembodiment of the present invention. As shown in FIG. 14, the colorfilters may comprise Ye, Mg, Cy, Gr (yellow, magenta, cyane and green)complementary color type filters. The Mg, Cy, Ye and Gr filters areformed into a sampling structure since they are disposed at thehorizontal directional pitch of 2PH, the vertical directional pitch of2Pv and the horizontal directional offset quantity is PH. Furthermore,the position at which is generated the carrier component of the imagepickup device, in which the thus-structured color filter array isdisposed, is arranged to be the same as that according to the firstembodiment shown in FIG. 6. Furthermore, the optical low-pass filteraccording to this embodiment is arranged similarly to that shown in FIG.7A. In a case of a solid image pickup device having about 760 effectivepixels in the horizontal direction, about 480 effective pixels in thevertical direction and an aspect ratio of 3:4, it holds the followingrelationship:

    1.2PH=Pv                                                   (7)

According to this embodiment, the relationship is arranged as follows:##EQU6## where symbol P1 denotes the distance in which the incidentalbeam is separated by the first optical member 31 shown in FIG. 7A andthe third optical member 33 and P2 denotes the distance in which theincidental beam is separated by the second optical member 32. Thetransfer characteristic displayed by means of a two-dimensionalfrequency space is shown in FIGS. 15A and 15B. Dotted lines 91a, 91b,92a, 92b, 93a and 93b show the frequencies at which a optical low-passfilter 200 traps. The optical low-pass, filter 200, as shown in FIGS.15A and 15B, comprises a first optical member 201 comprising abirefringence plate and a second optical member 202 comprising a phaseplate 203 and a birefringence plate 204. The birefringence plate 201separates an incidental light beam into two light beams in a directionof 45° from the horizontal direction by a distance P. The linearlypolarized light beam emitted from it is converted into a circularlypolarized light beam by the phase plate 203 before being separated in adirection of an angular degree of 135° from the horizontal direction bythe birefringence plate 204 by the distance P. As a result, it isdivided into four points of a rhomboid one side of which is P. The MTFcharacter of the above-described optical filter 200 is expressed bymeans of the two-dimensional frequency space. Dotted lines 121a, 121b,123a and 123b of FIG. 15B show the frequencies at which the opticallow-pass filter traps. As can be seen from FIG. 15B, carrier frequenciesof the chrominance signal are trapped. Therefore, the reflectiondistortion can satisfactorily be prevented such that the decay of theMTF within-15 dB takes place in the frequency region of |fH|=1/2PH. As aresult, a resolution substantially approximating the limit resolutionfrequency 1/2PH can be secured.

As can be clearly seen from FIGS. 15A and 15B, all of the carrierfrequencies of the luminance and chrominance signals can be trapped.Consequently, the reflection distortion can be satisfactorily prevented.Furthermore, calculating Equations (4), (7) and (8), the decay of theMTF within 15 dB takes place in a region which is about 96% of|fH|≦1/2PH. As a result, a resolution substantially approximating thelimit resolution frequency of 1/2PH can be secured.

According to both of the first and the second embodiments, the opticallow-pass filters are employed for both the luminance and chrominancesignals, the optical low-pass filters being capable of trapping at thecarrier frequency so as to make the MTF to be zero. However, the presentinvention is not limited to the carrier frequency. Any frequencies nearthe carrier frequency can be employed, but the MTF of which can besufficiently approximated to zero. In order to obtain it, the conditions(2) and (3) must be met.

A method of obtaining the image signal according to this embodiment willnow be described.

FIG. 16 is a block diagram of the signal process according to thisembodiment.

A CCD sensor 101a has a color filter array 101b composed of colorfilters of four types as shown in FIG. 14. An image signal read out ateach pixel by interlace scanning from the sensor 101a is subjected to again adjustment process by an AGC (Automatic Gain Adjustment Circuit)102 before it is A/D converted by an A/D converter 103 at a timing whichis in synchronization with the reading clock. It is preferable that theA/D converter 103 has a linear characteristic for preferably performingthe color forming process to be performed later. Furthermore, it actswith 8 bits or more in order to reduce the quantization error. Thesignal, which has been A/D converted, is written in a random accessmemory 125 so as to be subjected to a two-dimensional signal process tobe performed later, the signal being read out from the random accessmemory 125.

The luminance signals are read out from the random access memory 125 ina sequential order which corresponds to the reading of the pixels by theCCD. Furthermore, its high band components are detected by a high-passfilter 116 before it is added to the low luminance component YLobtainable from a method to be described later in an adder 117. Then, itis D/A converted by a D/A converter 118 before it is transmitted.

On the other hand, signals corresponding to the Mg, Cy, Ye and Gr colorfilters are read out from the random access memory before they aresupplied to four interpolation filters 106, 107, 108 and 109. As aresult, Mg, Cy, Ye and Gr color signals, which have been made tocoincide, are obtained.

The color signals thus-obtained are supplied to an RGB conversionportion 110 so as to be converted into R, G and B signals as a result ofthe following matrix calculation: ##EQU7##

The matrix A is formed into an optimized matrix constituted by threerows and four columns in order to approximate the spectrumcharacteristics Mg (λ), Gr (λ), Cy (λ) and Ye (λ) of Mg, Gr, Cy and Yeof the sensor 101a to ideal spectrum characteristics R (λ), G (λ) and B(λ) defined by the NTSC.

Then, a white balance portion 111 performs a white balancing operationin such a manner that R, G and B are converted into αR, G and βB inaccordance with color temperature information obtained from a whitebalance sensor 120.

Then, a γ-conversion portion 112 performs a γ-conversion of the RGBsignal by means of a table conversion.

A chrominance matrix portion 113 performs a conversion in accordancewith the standard of the NTSC as follows: ##EQU8##

As a result, the above-described luminance reduction component YL,chrominance signals R - Y and B - Y are generated. The chrominancesignals R - Y and B - Y are subsequently D/A converted by D/A converters114 and 115 so as to be transmitted. The luminance reduction componentYL is added to the high band component of the luminance detected by thehigh-pass filter 116 as described above before it is D/A converted bythe D/A converter 118 so as to be transmitted.

The structure of this embodiment may be structured by software by usinga DSP (Digital Signal Processor) or the like as an alternative to astructure formed into a hard-wired shape in accordance with the blockdiagram.

Although the first and second embodiments are capable of recording astill image, they may be adapted to video recording such as the videocamera.

As described above, according to this embodiment of the presentinvention, a color image pickup device can be provided in which thegeneration of false color can be prevented in both of the horizontal andthe vertical directions and in which a resolution of the luminancesignal approximated to the theorical limit can be obtained.

Furthermore, since the frequency of the luminance and the chrominancesignals to be trapped is relatively high, the thickness and the size ofthe optical low-pass filter can be reduced. As a result, a thin andcompact optical low-pass can be filter can be employed. Therefore, thesize of the overall body of its optical system can be reduced.

Furthermore, by employing a memory, the output timing from the odd fieldand the even field can be desirably set. Therefore, if the structureaccording to the present invention is adapted to, for example, a stillvideo camera, the frame photographing can be performed whilenecessitating the field head. Consequently, a reliable still videocamera with overall reduced cost can be manufactured.

Although the invention has been described in its preferred form with acertain degree of particularly, it is understood that the presentdisclosure of the preferred form has been changed in the details ofconstruction and the combination and arrangement of parts may beresorted to without departing from the spirit and the scope of theinvention as hereinafter claimed.

What is claimed is:
 1. A color image pickup apparatus comprising:animage pickup device in which a color filter array is provided, saidcolor filter array being composed of color filters of three or morecolors disposed in such a manner that, assuming that the horizontalscanning directional pitch of said color filters is PH and the verticalscanning directional pitch of the same is Pv, said color filters of thesame color are disposed at a horizontal scanning directional pitch of2PH and a vertical scanning directional pitch of 2PV while being offsetby PH in the horizontal scanning direction.
 2. A color image pickupapparatus according to claim 1, wherein an output from said image pickupdevice is temporarily recorded in a memory so that frame information isformed in response to a read signal from said memory.
 3. A color imagepickup apparatus comprising:an image pickup device having an opticallow-pass filter provided on the front surface thereof, said opticallow-pass filter being constituted by laminating a first optical memberfor dividing a light beam made incident upon by distance P1 while makingan angle of 45° from the horizontal scanning direction into two lightbeams, a second optical member for dividing a light beam made incidentupon by distance P2 while making an angle of 90° from the horizontalscanning direction into two light beams and a third optical member fordividing a light beam made incident upon by distance P1 while making anangle of 135° from the horizontal scanning direction into two lightbeams, said optical low-pass filter disposed meeting the followingconditions: ##EQU9##
 4. A color image pickup apparatus according toclaim 3, wherein an output from said image pickup device is temporarilyrecorded in a memory so that frame information is formed in response toa read signal from said memory.
 5. A color image pickup apparatuscomprising:a color filter array, from which the carrier of a chrominancesignal is not generated and which is disposed on the horizontalfrequency axis in a 2D-frequency space arranged in the horizontaldirection and the vertical direction; and an optical low-pass filter fortrapping a portion in the vicinity of the position of the carrier of aluminance signal and that of a chrominance signal in a 2D-frequencyspace arranged in the horizontal direction and the vertical direction,wherein said color filter array and said optical low-pass filter aredisposed on the front surface of said image pickup device.
 6. A colorimage pickup apparatus according to claim 5, wherein an output from saidimage pickup device is temporarily recorded in a memory so that frameinformation is formed in response to a read signal from said memory. 7.A color image pickup apparatus comprising:an image pickup device inwhich the horizontal directional pixel pitch is PH and the verticaldirectional pixel pitch is Pv; a color filter array formed into anoffset structure and provided for said image pickup device, said colorfilter array being composed of color filters of three or more colorsdisposed in such a manner that said color filters of the same color aredisposed at a horizontal scanning directional pitch of 2PH and avertical scanning directional pitch of 2Pv while being offset by PH inthe horizontal scanning direction. an optical low-pass filter composedof; a first optical member for dividing an incidental light beam intotwo light beams away from each other in a direction of 45° from thehorizontal direction by distance P; and a second optical member fordividing an incidental light beam into two light beams away from eachother in a direction of 90° from the direction in which said firstoptical member divides the light beam by distance P, said opticallow-pass filter being provided for an image pickup optical system andmeeting the following conditions: ##EQU10##
 8. A color image pickupapparatus according to claim 7 further comprising a signal processingmeans constituted by a memory for temporarily storing an output fromsaid image pickup device and a control portion for controlling saidmemory, said signal processing means forming frame information from thecontents stored in said memory.